XB-ART-44104Mol Brain. November 3, 2011; 4 40.
Regulation of chemotropic guidance of nerve growth cones by microRNA.
The small non-coding microRNAs play an important role in development by regulating protein translation, but their involvement in axon guidance is unknown. Here, we investigated the role of microRNA-134 (miR-134) in chemotropic guidance of nerve growth cones. We found that miR-134 is highly expressed in the neural tube of Xenopus embryos. Fluorescent in situ hybridization also showed that miR-134 is enriched in the growth cones of Xenopus spinal neurons in culture. Importantly, overexpression of miR-134 mimics or antisense inhibitors blocked protein synthesis (PS)-dependent attractive responses of Xenopus growth cones to a gradient of brain-derived neurotrophic factor (BDNF). However, miR-134 mimics or inhibitors had no effect on PS-independent bidirectional responses of Xenopus growth cones to bone morphogenic protein 7 (BMP7). Our data further showed that Xenopus LIM kinase 1 (Xlimk1) mRNA is a potential target of miR-134 regulation. These findings demonstrate a role for miR-134 in translation-dependent guidance of nerve growth cones. Different guidance cues may act through distinct signaling pathways to elicit PS-dependent and -independent mechanisms to steer growth cones in response to a wide array of spatiotemporal cues during development.
PubMed ID: 22051374
PMC ID: PMC3217933
Article link: Mol Brain.
Grant support: DA027080 NIDA NIH HHS , GM083889 NIGMS NIH HHS , Wellcome Trust , 085314 Wellcome Trust , WT085314 Wellcome Trust
Genes referenced: actl6a bdnf bmp7.1 ctrl dnai1 kit limk1 mapk1 mtor
Article Images: [+] show captions
|Figure 2. Enrichment of miR-134 in Xenopus growth cones. Fluorescence in situ hybridization was used to detect miR-134 in cultured Xenopus spinal neurons using a LNA probe (A) or scrambled probe (B). Phase contrast images of the growth cones are shown as insets. Arrows indicate the miR-134 puncta in the lamellipodia and filopodia. Scale bars: 10 μm.|
|Figure 5. Detection of Xenopus limk1 in Xenopus neurons. (A) RT-PCR detection of Xlimk1 mRNA from RNA samples extracted from Stage 20-22 Xenopus neural tube tissues using specific primers. RNA samples were processed without (-RT) and with reverse transcriptase (RT). (B) Representative fluorescence images of cultured Xenopus growth cones labeled using a specific antibody against LIMK1. (C) Detection of Xlimk1 mRNA in Xenopus growth cones by fluorescence in situ hybridization. Top panels are the differential interference contrast (DIC) images of the growth cones. Bottom panels are the FISH images of Xenopus growth cones labeled with digoxigenin-conjugated probes (three probes, ~50 nt each) that are specifically complementary to different parts of the coding region of Xlimk1 mRNA. The reverse probes were used as the control. Scale: 10 μm.|
|Figure 7. The schematic diagram shows a proposed model on how different cues might act through PS-dependent and -independent pathways to regulate growth cone steering. BMP7 acts as bidirectional guidance molecular through phosphorylation regulation of actin depolymerizing factor (ADF)/cofilin (AC). We propose that BDNF gradients release the inhibition of translation by miR-134 and induce the local translation of Xlimk1 in an asymmetric way, leading to the asymmetric modification of the actin dynamics for growth cone steering. BDNF also acts to elicit asymmetric β-actin translation, which could plausibly operate in parallel to or in concert with the miR-134 regulation of LIMK1 translation for growth cone turning. Future experiments are required to test this model. For simplicity, the mTOR pathway is not depicted in the model.|